The present disclosure relates to power converters and more particularly to power converters using active clamp flyback topologies.
Flyback converters are often used in alternating current to direct current (AC/DC) conversion. In some flyback architectures, an active clamp capacitor in series with a synchronously driven high side transistor is connected in parallel to the primary winding of the flyback transformer to smooth the output of the converter. The resulting converter is known as an active clamp flyback (ACF) converter.
When the ACF converter operates in steady state, it maintains the clamp voltage across the clamp capacitor (VCLAMP) at approximately a certain value but with ripple around this value due to charging and discharging caused by leakage inductance current. If a fault happens that prevents the high side transistor from switching, the ACF converter continues to operate like a conventional flyback converter. However the MOSFET has a parasitic body diode that results from connecting the body to the source terminal. This body diode causes VCLAMP to increase since there is no discharge path. This buildup in voltage across the clamp capacitor will eventually cause the ACF converter to be damaged or otherwise to fail.
The use of the same reference symbols in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well.